1. Field of the Invention
The present invention relates generally to solar lighting apparatuses and, more particularly, to a solar lighting apparatus which can diffuse and refract solar light, emitted from an end of an optical fiber, beyond a predetermined angle, and can diffuse and reflect some of the solar light.
2. Description of the Related Art
Generally, optical fibers made of glass or plastic are used to transmit solar light, that is, natural light, that is being focused on an area of a predetermined size or less, to a place to be illuminated. Such an optical fiber comprises a core and a cladding made of material having a refractive index less than that of the core. Solar light that enters a first end of the optical fiber is total-reflected on a boundary surface between the core and the cladding and is emitted out of a second end of the optical fiber towards the place where illumination is needed. The reason that optical fibers are used in apparatuses using solar light for illumination despite the fact that optical fibers are very expensive is that during optical transmission the optical loss rate can be minimized.
As such, the optical fiber has the advantage of the optical loss rate being minimized during optical transmission, but it is disadvantageous in that the light-receiving angle is limited to a predetermined degree because of the total-reflection characteristics of the optical fiber. Limiting the light-receiving angle of solar light entering the first end of the optical fiber implies that the angle of solar light emitted from the second end of the optical fiber is also limited. Thus, solar light emitted from the second end of the optical fiber is excessively focused on a specific portion of the place where illumination is needed. Such a phenomenon in which light emitted from the optical fiber is focused only on a specific portion is a fundamental problem of optical fiber. In this art, using a diffusion lens has been attempted in order to solve this problem. Representative examples were proposed in Korean Patent Registration No. 0401363 and Korean Utility Model Registration No. 0318554.
The construction that the former proposes is a construction such that solar light emitted from the end of the optical fiber is scattered-reflected by a lens. The construction proposed by the latter is such that light emitted from the end of the optical fiber is diffused by a lens the surface of which has been finely treated by sanding. According to these conventional techniques, solar light emitted from the end of the optical fiber can be somewhat diffused by the lens before being transmitted to a place where illumination is needed. However, the lenses used in the conventional techniques are typical convex lenses (an improved type of convex lenses). It is difficult for this lens structure to increase the angle at which solar light is diffused to the expected degree. Another practical method to solve this disadvantage is required.